Ball and socket joints are used in a variety of applications, including rack and pinion inner tie rod socket assemblies, steering knuckles, drag links, and connecting rod assemblies. Ball and socket joints typically include a generally cylindrical socket member adapted to receive one or more bearings together with a head of a ball stud. The bearing reduces the degree of friction between the socket and ball stud head and is sometimes used to compensate for wear between the stud and socket member by way of a compression preload. However, a small degree of friction is necessary for the ball joint to operate smoothly.
Current light-weight vehicle designs dictate the use of low friction plastic bearings for steering and suspension ball and socket joints. The use of plastic bearings provide a significant increase in load shock dampening capability and system compliance than previous known metal bearing joints. However, there are drawbacks to the use of plastic bearings. A significant amount of assembly pre-load force must be exerted against the plastic material to obtain low end motion of the stud. However, low end motion results in higher torque values.
To achieve a low stud rotating torque value, a lower assembly preload can be utilized but this results in unacceptably high end motion of the stud. In an effort to achieve a low torque, low end motion ball and socket joint, bearings are known which incorporate additives such as polytetraflouroethylene (PTFE), or the like, to reduce friction, and thereby permit the use of significant preloads to control the level of end motion. Such bearings are only marginally successful in producing low torque and low end motion ball and socket joints. Further, the use of additives undesirably increases manufacturing costs.